1. Field of Invention
The invention relates to dye lasers; more particularly, it relates to the use of a new class of dyes as lasing media for organic dye lasers.
2. Description of the Prior Art
Organic dye lasers are known in the art and are exemplified by U.S. Pat. No. 3,493,885 to Peter P. Sorokin and commonly assigned to the assignee of the present invention. These dye lasers have certain advantages over the more conventional gas or solid state lasers. Because of their broad band fluorescence characteristics, they can be tuned to emit over a range of wavelengths. These lasers are also more economical than the gas or solid state lasers.
Several dyes are useful in dye lasers, such as metal phthalocyanines disclosed in the above-mentioned patent to Peter P. Sorokin, bridged enamine and allopolar cyanine dyes, U.S. Pat. No. 3,774,122 to Frank G. Webster and polymethine dyes as disclosed in U.S. Pat. No. 3,798,566 to William C. McColgin and Frank G. Webster. The above-mentioned dyes all emit in the near infra-red region of the spectrum, i.e., at about 600 nm. to about 1.mu.. Further these dyes are subject to photodegradation over a relatively short period of time, e.g., 7 to 10 days. The dyes of the present invention have been found not to photodegrade after use of periods of a month or more.
A particularly suitable laser structure adapted for organic dye liquid laser is described by Sorokin et al., IBM Journal, V. 11, p. 148 (1967). The described structure includes an optically resonant cavity containing a reservoir of a liquid laser medium or a liquid laser body dispersed within a thin-walled quartz cylinder. The reservoir is part of a closed system through which the dye solution is circulated during lasing operation. There is also provided a pumping source which subjects the dye to bombardment of electrons or illuminates it with a high energy source. Such pumping sources can be selected from giant pulse lasers, xenon and argon arc flash tubes as well as arc discharge tubes containing only air or other gaseous mixtures.
The above-mentioned prior art dyes placed in a suitable laser structure and pumped with an illuminating source such as a nitrogen laser emit light in the yellow, red and near infra-red region of the spectrum. Few if any known dyes when subjected as above emit light in the violet and near ultra-violet region of the spectrum. Those dyes which may be found to emit in the violet and near ultra-violet region do so weakly, e.g., they have outputs of less than 20 kilowatts. It is important to provide dyes which will have strong emission in the violet and ultra-violet region of the spectrum, e.g., outputs of 50 kilowatts or more.
Another suitable laser structure in which the laser dyes of the present invention can be used is that disclosed in U.S. Pat. No. 3,816,754, and patent application Ser. No. 458,144, to J. R. Lankard et al., and both being assigned to the same assignee as is the present invention. The above patent and patent application describe a tunable infra-red/ultra-violet laser. In FIG. 1 thereof, there is shown a pair of tunable dye lasers, wherein one is made to emit at a first frequency f.sub.L, called the pump frequency, and the other emits a second frequency f.sub.P. The two output beams f.sub.L and f.sub.P are combined by mirrors or prisms into a colinear beam, which is focused into a heat pipe oven containing an alkali metal vapor. Frequency f.sub.L creates a third frequency f.sub.S in the vapor via an electronic stimulated Raman effect. Frequency f.sub.P mixes with f.sub.S and f.sub.L to produce f.sub.R, where f.sub.R = f.sub.L - f.sub.S .-+. f.sub.P. Since f.sub.L - f.sub.S equals a constant, K, the produced frequency f.sub.R = K .-+. f.sub.P. Since the difference K - f.sub.P can easily be made quite small, a tuning range extending into the far infra-red is practicable. The sum K + f.sub.P extends the tuning range to higher frequencies, i.e., into the ultra-violet. To obtain frequencies in the ultra-violet range of the spectrum, laser dyes of the present invention may be used to generate the frequency f.sub.P.
Accordingly, it is an important object of this invention to provide organic dyes which lase in the violet and near ultra-violet region of the spectrum.
It is a further object to provide a class of 2,4,6 trisubstituted pyridine dyes which are useful as lasing media.
The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawing.